1. Field of the Invention
The present invention relates to display equipment and an art related thereto.
2. Description of the Related Art
Display equipment that employs various types of display devices have been in customary use. One known type of display equipment heretofore includes a display device such as a color LCD and a color plasma display, in which three light-emitting elements for illuminating three primary colors (RGB) are aligned in certain sequence to form a pixel. A plurality of the pixels are aligned in series in a first direction, thereby forming a line. A plurality of the lines are aligned in a second direction perpendicular to the first direction, thereby forming a display screen on the display device.
A large number of display devices having display screens reduced in size to a degree that they fail to provide a sufficiently fine display. This problem is commonly seen in the display devices disposed in, e.g., a cellular phone and a mobile computer. In such display devices, small characters and photographs, or complicated pictures, are often smeared and rendered obscure in sharpness.
In order to provide improved display sharpness in such a small display screen, a reference entitled “Sub-Pixel Font-Rendering Technology” is open to the public on the Internet. The reference discusses a per sub-pixel display based on a pixel formed by three light-emitting elements (RGB). The present Inventors downloaded the reference on Jun. 19, 2000 from a web site on the world wide web posted by Gibson Research Corporation.
The above technology is now described with reference to FIGS. 38 to 42. In the following description, an alphabetic character “A” is used as an example of a displayed image.
FIG. 38 is a simulated illustration, showing a line that includes a chain of pixels, each of which consists of the three light-emitting elements. In FIG. 38, a horizontal direction, or a direction in which the light-emitting elements are aligned with each other, is called a first direction, while a vertical direction perpendicular to the first direction is referred to as a second direction.
In the prior art as well as the present invention, the light-emitting elements are not limited to alignment in the order of R. G, and B, but may be arranged serially in any other alphabetical sequence.
A plurality of the pixels, each of which is formed by the three light-emitting elements, is arranged in a row in the first direction in order to provide a line. A plurality of the lines are aligned with each other in the second direction, thereby providing a display screen on the display device.
The sub-pixel technology as discussed above addresses an original image as illustrated in, e.g., FIG. 39. In this example, the character “A” is displayed over a display screen area that consists of seven pixels-by-seven pixels in the horizontal and vertical (first and second) directions, respectively. Meanwhile, a font having a resolution horizontally magnified as three times as large as that of the previous character is provided as illustrated in FIG. 40 in order to provide a per sub-pixel display. In FIG. 40, assuming that each of the light-emitting elements (RGB) is viewed as a single pixel, the character “A” is displayed over a display screen area that consists of twenty-one pixels (=7*3 pixels) horizontally by seven pixels vertically.
As illustrated in FIG. 41, a color is determined for each of the pixels of FIG. 39, not the pixels in FIG. 40. However, color irregularities occur when the determined colors are displayed without being processed. The determined colors must be filtered using factors as shown in FIG. 42(a) in order to avoid the color irregularities. As illustrated in FIG. 42(a), the factors are correlated with luminance. For example, a central target sub-pixel is multiplied by a factor of 3/9. Contiguously adjacent sub-pixels next to the central sub-pixel are multiplied by a factor of 2/9. Sub-pixels next to the contiguously adjacent sub-pixels are multiplied by a factor of 1/9. This is the manner in which the luminance of each of the sub-pixels is adjusted.
Filtering the colored pixels as illustrated in FIG. 41 results in pixels as shown in FIG. 42(b). In FIG. 42(b), colors are adjusted in such a manner that yellow, red, cyan, and blue are changed to light yellow, light red, light cyan, and light blue, respectively.
The luminance of the sub-pixels of the filtered image is allocated to the light-emitting elements of FIG. 40, thereby displaying the image on a per sub-pixel basis.